Maintenance isn't always as you expect it to be. It is calculated from your average fleet age, so if you have one really old aircraft, your maintenance will rise because of that aircraft. You can see your average fleet age when clicking on the tab 'Aircraft'. Make sure to keep it under 3 years, and preferably less than two.
The game does not currently support cargo, although most airports have cargo data ready for when it is done. Just don't expect it to be done in the near future.
